Because fluorescent lamps cannot be simply dimmed with a phase control like incandescent lamps, numerous suggestions have been made for reducing the brightness by means of group circuits or other methods in residential or business quarters.
This applies especially to fluorescent compact lamps where the fluorescent lamp with a ballast is inserted in the normal lamp socket and therefore only the two mains supply lines are available for modulating the brightness.
For example, the German patent DE 40 37 948 described an arrangement where the compact lamp is switched to two bi-stable switching conditions by short interruptions of the power supply. This arrangement was used in practice but is not satisfactory because it is not adequately comparable with the function of a continually controllable dimmer.
U.S. Pat. No. 5,068,576 introduced another dimmer switch for a fluorescent lamp where a simple two-wire connection is arranged between the dimmer switch and the fluorescent lamp. The control of the logical circuit is performed via the change of the input voltage of a voltage regulator. A microcomputer influences the voltage amount through digital signals. A phase cutting control was described where complete half waves are cut off from the mains alternating voltage. This entails the disadvantage that the cut half waves cause the fluorescent lamp to flicker when dimmed.